# Copyright The OpenTelemetry Authors
# SPDX-License-Identifier: Apache-2.0

"""
Usage
-----

.. code-block:: python

    import fastapi
    from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor

    app = fastapi.FastAPI()

    @app.get("/foobar")
    async def foobar():
        return {"message": "hello world"}

    FastAPIInstrumentor.instrument_app(app)

Configuration
-------------

Exclude lists
*************
To exclude certain URLs from tracking, set the environment variable ``OTEL_PYTHON_FASTAPI_EXCLUDED_URLS``
(or ``OTEL_PYTHON_EXCLUDED_URLS`` to cover all instrumentations) to a string of comma delimited regexes that match the
URLs.

For example,

::

    export OTEL_PYTHON_FASTAPI_EXCLUDED_URLS="client/.*/info,healthcheck"

will exclude requests such as ``https://site/client/123/info`` and ``https://site/xyz/healthcheck``.

You can also pass comma delimited regexes directly to the ``instrument_app`` method:

.. code-block:: python

    FastAPIInstrumentor.instrument_app(app, excluded_urls="client/.*/info,healthcheck")

Request/Response hooks
**********************

This instrumentation supports request and response hooks. These are functions that get called
right after a span is created for a request and right before the span is finished for the response.

- The server request hook is passed a server span and ASGI scope object for every incoming request.
- The client request hook is called with the internal span, and ASGI scope and event when the method ``receive`` is called.
- The client response hook is called with the internal span, and ASGI scope and event when the method ``send`` is called.

.. code-block:: python

    from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
    from opentelemetry.trace import Span
    from typing import Any

    def server_request_hook(span: Span, scope: dict[str, Any]):
        if span and span.is_recording():
            span.set_attribute("custom_user_attribute_from_request_hook", "some-value")

    def client_request_hook(span: Span, scope: dict[str, Any], message: dict[str, Any]):
        if span and span.is_recording():
            span.set_attribute("custom_user_attribute_from_client_request_hook", "some-value")

    def client_response_hook(span: Span, scope: dict[str, Any], message: dict[str, Any]):
        if span and span.is_recording():
            span.set_attribute("custom_user_attribute_from_response_hook", "some-value")

    FastAPIInstrumentor().instrument(server_request_hook=server_request_hook, client_request_hook=client_request_hook, client_response_hook=client_response_hook)

Capture HTTP request and response headers
*****************************************
You can configure the agent to capture specified HTTP headers as span attributes, according to the
`semantic conventions <https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-spans.md#http-server-span>`_.

Request headers
***************
To capture HTTP request headers as span attributes, set the environment variable
``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST`` to a comma delimited list of HTTP header names,
or pass the ``http_capture_headers_server_request`` keyword argument to the ``instrument_app`` method.

For example using the environment variable,
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST="content-type,custom_request_header"

will extract ``content-type`` and ``custom_request_header`` from the request headers and add them as span attributes.

Request header names in FastAPI are case-insensitive. So, giving the header name as ``CUStom-Header`` in the environment
variable will capture the header named ``custom-header``.

Regular expressions may also be used to match multiple headers that correspond to the given pattern.  For example:
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST="Accept.*,X-.*"

Would match all request headers that start with ``Accept`` and ``X-``.

To capture all request headers, set ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST`` to ``".*"``.
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST=".*"

The name of the added span attribute will follow the format ``http.request.header.<header_name>`` where ``<header_name>``
is the normalized HTTP header name (lowercase, with ``-`` replaced by ``_``). The value of the attribute will be a
single item list containing all the header values.

For example:
``http.request.header.custom_request_header = ["<value1>", "<value2>"]``

Response headers
****************
To capture HTTP response headers as span attributes, set the environment variable
``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE`` to a comma delimited list of HTTP header names,
or pass the ``http_capture_headers_server_response`` keyword argument to the ``instrument_app`` method.

For example using the environment variable,
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE="content-type,custom_response_header"

will extract ``content-type`` and ``custom_response_header`` from the response headers and add them as span attributes.

Response header names in FastAPI are case-insensitive. So, giving the header name as ``CUStom-Header`` in the environment
variable will capture the header named ``custom-header``.

Regular expressions may also be used to match multiple headers that correspond to the given pattern.  For example:
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE="Content.*,X-.*"

Would match all response headers that start with ``Content`` and ``X-``.

To capture all response headers, set ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE`` to ``".*"``.
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE=".*"

The name of the added span attribute will follow the format ``http.response.header.<header_name>`` where ``<header_name>``
is the normalized HTTP header name (lowercase, with ``-`` replaced by ``_``). The value of the attribute will be a
list containing the header values.

For example:
``http.response.header.custom_response_header = ["<value1>", "<value2>"]``

Sanitizing headers
******************
In order to prevent storing sensitive data such as personally identifiable information (PII), session keys, passwords,
etc, set the environment variable ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SANITIZE_FIELDS``
to a comma delimited list of HTTP header names to be sanitized, or pass the ``http_capture_headers_sanitize_fields``
keyword argument to the ``instrument_app`` method.

Regexes may be used, and all header names will be matched in a case-insensitive manner.

For example using the environment variable,
::

    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SANITIZE_FIELDS=".*session.*,set-cookie"

will replace the value of headers such as ``session-id`` and ``set-cookie`` with ``[REDACTED]`` in the span.

Note:
    The environment variable names used to capture HTTP headers are still experimental, and thus are subject to change.

API
---
"""

from __future__ import annotations

import functools
import logging
import types
from typing import Any, Collection, Literal
from weakref import WeakSet as _WeakSet

import fastapi
from starlette.applications import Starlette
from starlette.background import BackgroundTask
from starlette.middleware.errors import ServerErrorMiddleware
from starlette.routing import Match, Route
from starlette.types import ASGIApp, Receive, Scope, Send

from opentelemetry.instrumentation._semconv import (
    _get_schema_url,
    _OpenTelemetrySemanticConventionStability,
    _OpenTelemetryStabilitySignalType,
    _StabilityMode,
)
from opentelemetry.instrumentation.asgi import OpenTelemetryMiddleware
from opentelemetry.instrumentation.asgi.types import (
    ClientRequestHook,
    ClientResponseHook,
    ServerRequestHook,
)
from opentelemetry.instrumentation.fastapi.package import _instruments
from opentelemetry.instrumentation.fastapi.version import __version__
from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
from opentelemetry.metrics import MeterProvider, get_meter
from opentelemetry.semconv.attributes.http_attributes import HTTP_ROUTE
from opentelemetry.trace import TracerProvider, get_current_span, get_tracer
from opentelemetry.trace.status import Status, StatusCode
from opentelemetry.util.http import (
    get_excluded_urls,
    parse_excluded_urls,
    sanitize_method,
)

_excluded_urls_from_env = get_excluded_urls("FASTAPI")
_logger = logging.getLogger(__name__)


class FastAPIInstrumentor(BaseInstrumentor):
    """An instrumentor for FastAPI

    See `BaseInstrumentor`
    """

    _original_fastapi = None

    @staticmethod
    def instrument_app(
        app: fastapi.FastAPI,
        server_request_hook: ServerRequestHook = None,
        client_request_hook: ClientRequestHook = None,
        client_response_hook: ClientResponseHook = None,
        tracer_provider: TracerProvider | None = None,
        meter_provider: MeterProvider | None = None,
        excluded_urls: str | None = None,
        http_capture_headers_server_request: list[str] | None = None,
        http_capture_headers_server_response: list[str] | None = None,
        http_capture_headers_sanitize_fields: list[str] | None = None,
        exclude_spans: list[Literal["receive", "send"]] | None = None,
    ):  # pylint: disable=too-many-locals
        """Instrument an uninstrumented FastAPI application.

        Args:
            app: The fastapi ASGI application callable to forward requests to.
            server_request_hook: Optional callback which is called with the server span and ASGI
                          scope object for every incoming request.
            client_request_hook: Optional callback which is called with the internal span, and ASGI
                          scope and event which are sent as dictionaries for when the method receive is called.
            client_response_hook: Optional callback which is called with the internal span, and ASGI
                          scope and event which are sent as dictionaries for when the method send is called.
            tracer_provider: The optional tracer provider to use. If omitted
                the current globally configured one is used.
            meter_provider: The optional meter provider to use. If omitted
                the current globally configured one is used.
            excluded_urls: Optional comma delimited string of regexes to match URLs that should not be traced.
            http_capture_headers_server_request: Optional list of HTTP headers to capture from the request.
            http_capture_headers_server_response: Optional list of HTTP headers to capture from the response.
            http_capture_headers_sanitize_fields: Optional list of HTTP headers to sanitize.
            exclude_spans: Optionally exclude HTTP `send` and/or `receive` spans from the trace.
        """
        if not hasattr(app, "_is_instrumented_by_opentelemetry"):
            app._is_instrumented_by_opentelemetry = False

        if not getattr(app, "_is_instrumented_by_opentelemetry", False):
            # initialize semantic conventions opt-in if needed
            _OpenTelemetrySemanticConventionStability._initialize()
            sem_conv_opt_in_mode = _OpenTelemetrySemanticConventionStability._get_opentelemetry_stability_opt_in_mode(
                _OpenTelemetryStabilitySignalType.HTTP,
            )
            if excluded_urls is None:
                excluded_urls = _excluded_urls_from_env
            else:
                excluded_urls = parse_excluded_urls(excluded_urls)
            tracer = get_tracer(
                __name__,
                __version__,
                tracer_provider,
                schema_url=_get_schema_url(sem_conv_opt_in_mode),
            )
            meter = get_meter(
                __name__,
                __version__,
                meter_provider,
                schema_url=_get_schema_url(sem_conv_opt_in_mode),
            )

            def build_middleware_stack(self: Starlette) -> ASGIApp:
                # Define an additional middleware for exception handling
                # Normally, `opentelemetry.trace.use_span` covers the recording of
                # exceptions into the active span, but `OpenTelemetryMiddleware`
                # ends the span too early before the exception can be recorded.
                class ExceptionHandlerMiddleware:
                    def __init__(self, app):
                        self.app = app

                    async def __call__(
                        self, scope: Scope, receive: Receive, send: Send
                    ) -> None:
                        try:
                            await self.app(scope, receive, send)
                        except Exception as exc:  # pylint: disable=broad-exception-caught
                            span = get_current_span()
                            if span.is_recording():
                                span.record_exception(exc)
                                span.set_status(
                                    Status(
                                        status_code=StatusCode.ERROR,
                                        description=f"{type(exc).__name__}: {exc}",
                                    )
                                )
                            raise

                # For every possible use case of error handling, exception
                # handling, trace availability in exception handlers and
                # automatic exception recording to work, we need to make a
                # series of wrapping and re-wrapping middlewares.

                # First, grab the original middleware stack from Starlette. It
                # comprises a stack of
                # `ServerErrorMiddleware` -> [user defined middlewares] -> `ExceptionMiddleware`
                inner_server_error_middleware: ServerErrorMiddleware = (  # type: ignore
                    self._original_build_middleware_stack()  # type: ignore
                )

                if not isinstance(
                    inner_server_error_middleware, ServerErrorMiddleware
                ):
                    # Oops, something changed about how Starlette creates middleware stacks
                    _logger.error(
                        "Skipping FastAPI instrumentation due to unexpected middleware stack: expected %s, got %s",
                        ServerErrorMiddleware.__name__,
                        type(inner_server_error_middleware),
                    )
                    return inner_server_error_middleware

                # We take [user defined middlewares] -> `ExceptionHandlerMiddleware`
                # out of the outermost `ServerErrorMiddleware` and instead pass
                # it to our own `ExceptionHandlerMiddleware`
                exception_middleware = ExceptionHandlerMiddleware(
                    inner_server_error_middleware.app
                )

                # Now, we create a new `ServerErrorMiddleware` that wraps
                # `ExceptionHandlerMiddleware` but otherwise uses the same
                # original `handler` and debug setting. The end result is a
                # middleware stack that's identical to the original stack except
                # all user middlewares are covered by our
                # `ExceptionHandlerMiddleware`.
                error_middleware = ServerErrorMiddleware(
                    app=exception_middleware,
                    handler=inner_server_error_middleware.handler,
                    debug=inner_server_error_middleware.debug,
                )

                # Finally, we wrap the stack above in our actual OTEL
                # middleware. As a result, an active tracing context exists for
                # every use case of user-defined error and exception handlers as
                # well as automatic recording of exceptions in active spans.
                otel_middleware = OpenTelemetryMiddleware(
                    error_middleware,
                    excluded_urls=excluded_urls,
                    default_span_details=_get_default_span_details,
                    server_request_hook=server_request_hook,
                    client_request_hook=client_request_hook,
                    client_response_hook=client_response_hook,
                    # Pass in tracer/meter to get __name__and __version__ of fastapi instrumentation
                    tracer=tracer,
                    meter=meter,
                    http_capture_headers_server_request=http_capture_headers_server_request,
                    http_capture_headers_server_response=http_capture_headers_server_response,
                    http_capture_headers_sanitize_fields=http_capture_headers_sanitize_fields,
                    exclude_spans=exclude_spans,
                )

                # Ultimately, wrap everything in another default
                # `ServerErrorMiddleware` (w/o user handlers) so that any
                # exceptions raised in `OpenTelemetryMiddleware` are handled.
                #
                # This should not happen unless there is a bug in
                # OpenTelemetryMiddleware, but if there is we don't want that to
                # impact the user's application just because we wrapped the
                # middlewares in this order.
                return ServerErrorMiddleware(
                    app=otel_middleware,
                )

            app._original_build_middleware_stack = app.build_middleware_stack
            app.build_middleware_stack = types.MethodType(
                functools.wraps(app.build_middleware_stack)(
                    build_middleware_stack
                ),
                app,
            )

            if not hasattr(BackgroundTask, "_otel_original_call"):
                BackgroundTask._otel_original_call = BackgroundTask.__call__

                async def traced_call(self):
                    span_name = f"BackgroundTask {getattr(self.func, '__name__', self.func.__class__.__name__)}"
                    with tracer.start_as_current_span(span_name):
                        return await BackgroundTask._otel_original_call(self)

                BackgroundTask.__call__ = traced_call

            app._is_instrumented_by_opentelemetry = True
            if app not in _InstrumentedFastAPI._instrumented_fastapi_apps:
                _InstrumentedFastAPI._instrumented_fastapi_apps.add(app)
        else:
            _logger.warning(
                "Attempting to instrument FastAPI app while already instrumented"
            )

    @staticmethod
    def uninstrument_app(app: fastapi.FastAPI):
        original_build_middleware_stack = getattr(
            app, "_original_build_middleware_stack", None
        )
        if original_build_middleware_stack:
            app.build_middleware_stack = original_build_middleware_stack
            del app._original_build_middleware_stack
        app.middleware_stack = app.build_middleware_stack()

        if hasattr(BackgroundTask, "_otel_original_call"):
            BackgroundTask.__call__ = BackgroundTask._otel_original_call
            del BackgroundTask._otel_original_call

        app._is_instrumented_by_opentelemetry = False

        # Remove the app from the set of instrumented apps to avoid calling uninstrument twice
        # if the instrumentation is later disabled or such
        # Use discard to avoid KeyError if already GC'ed
        _InstrumentedFastAPI._instrumented_fastapi_apps.discard(app)

    def instrumentation_dependencies(self) -> Collection[str]:
        return _instruments

    def _instrument(self, **kwargs: Any):
        self._original_fastapi = fastapi.FastAPI
        _InstrumentedFastAPI._instrument_kwargs = kwargs
        fastapi.FastAPI = _InstrumentedFastAPI

    def _uninstrument(self, **kwargs):
        # Create a copy of the set to avoid RuntimeError during iteration
        instances_to_uninstrument = list(
            _InstrumentedFastAPI._instrumented_fastapi_apps
        )
        for instance in instances_to_uninstrument:
            self.uninstrument_app(instance)
        _InstrumentedFastAPI._instrumented_fastapi_apps.clear()
        fastapi.FastAPI = self._original_fastapi


class _InstrumentedFastAPI(fastapi.FastAPI):
    _instrument_kwargs: dict[str, Any] = {}

    # Track instrumented app instances using weak references to avoid GC leaks
    _instrumented_fastapi_apps: _WeakSet[fastapi.FastAPI] = _WeakSet()
    _sem_conv_opt_in_mode = _StabilityMode.DEFAULT

    def __init__(self, *args: Any, **kwargs: Any):
        super().__init__(*args, **kwargs)
        FastAPIInstrumentor.instrument_app(
            self, **_InstrumentedFastAPI._instrument_kwargs
        )
        _InstrumentedFastAPI._instrumented_fastapi_apps.add(self)


def _get_route_details(scope):
    """
    Function to retrieve Starlette route from scope.

    TODO: there is currently no way to retrieve http.route from
    a starlette application from scope.
    See: https://github.com/encode/starlette/pull/804

    Args:
        scope: A Starlette scope
    Returns:
        A string containing the route or None
    """
    app = scope["app"]
    route = None

    for starlette_route in app.routes:
        match, _ = (
            Route.matches(starlette_route, scope)
            if isinstance(starlette_route, Route)
            else starlette_route.matches(scope)
        )
        if match == Match.FULL:
            try:
                route = starlette_route.path
            except AttributeError:
                # routes added via host routing won't have a path attribute
                route = scope.get("path")
            break
        if match == Match.PARTIAL:
            route = starlette_route.path
    return route


def _get_default_span_details(scope):
    """
    Callback to retrieve span name and attributes from scope.

    Args:
        scope: A Starlette scope
    Returns:
        A tuple of span name and attributes
    """
    route = _get_route_details(scope)
    method = sanitize_method(scope.get("method", "").strip())
    attributes = {}
    if method == "_OTHER":
        method = "HTTP"
    if route:
        attributes[HTTP_ROUTE] = route
    if method and route:  # http
        span_name = f"{method} {route}"
    elif route:  # websocket
        span_name = route
    else:  # fallback
        span_name = method
    return span_name, attributes
